Water has been used as a transportation medium in moving a product from a production locus to a processing or use locus for many years. A variety of materials can be made to float or become suspended or dissolved in water have been transported using a moving aqueous stream. have been transported using a moving aqueous stream. Examples of such materials include products of the lumber industry, coal in a coal slurry, agricultural products such as fruits and vegetables, particulate products of aqueous polymerization, and others too numerous to mention. One consistent design characteristic of these systems is the use of a closed loop aqueous stream returning the aqueous medium to its origin. The aqueous stream that transports the material from a production locus to a processing locus is often returned, without product, to the production locus for new product for transport. Such recycled water streams that are continually reused acquire a soil load that can support the growth of microbial populations and in particular slime producing microorganisms. Such closed flow water systems can obtain and accumulate substantial concentrations of impurities from the environment and from the product transported in the closed loop system. Such a challenge soil load can pose even more substantial problems in the instance that the product is of biological origin including products such as wood, wood fiber, fruits, vegetables, etc. or other products comprising substantial quantities of carbohydrate, lipid or proteinaceous compositions that can act as a food source for microorganisms. A need for effective antimicrobial agents and processes is apparent to prevent or reduce microbial populations.
Ideally, an antimicrobial agent or compound used in such a system will have several important properties in addition to its antimicrobial efficacy. The compound or agent should have no residual antimicrobial activity on the food after processing. Residual activity implies the presence of a film of antimicrobial material which will continue to have antimicrobial effect which may require further rinsing of the food product. The antimicrobial agent preferably should also be odor free to prevent transfer of undesirable odors onto food stuffs. The antimicrobial agent should also be composed of direct food additive materials which will not effect food if contamination occurs, nor effect humans should incidental ingestion result. In addition, the antimicrobial agent should preferably be composed of, or should result in naturally occurring or innocuous ingredients, which are chemically compatible with the environment and cause no concerns for toxic residues within the flume water.
One common aqueous transport system comprises a flume system. Such systems are used in agriculture to transport an agricultural product such as fruits or vegetables from a production locus, typically a farm field or garden plot to a processing locus, for washing and packing using an aqueous stream. The fruits or vegetables are cleaned, treated and packed for distribution at the processing locus. Such flume systems can contain large volumes of water flowing at a rate of about 20 to 4000 liters per minute. Such flume systems can transport substantial quantities of fruits or vegetables from a production locus to a processing locus. Such systems can transport about 10 to 1000 pounds of fruits or vegetables per minute or more, on a continuous basis during production operations. Such flume streams inherently become contaminated with soil, fruit and vegetable fragments, plant fragments, and other agricultural by-products. Such a flume stream is a potent medium for promoting the growth of microorganisms. Untreated flume water can rapidly become contaminated with large microbial populations. As a result of the growth of slime forming microorganisms, the surfaces of the aqueous system can rapidly be coated with slime producing colonies and the slime by-product.
The challenge soil load can comprise a substantial proportion of the aqueous stream, commonly about 0.1 to 20 wt. % of the aqueous stream, most commonly about 1-15 wt. % of the aqueous stream.
The most common treatment to reduce the populations of such microorganisms comprises contacting the flume stream, at any arbitrary position in the closed loop, with chlorine (Cl.sub.2) or a chlorine containing or yielding antimicrobial composition. Such antimicrobials include chlorine gas (Cl.sub.2), chlorine dioxide (ClO.sub.2) sodium hypochlorite (NaOCl), chlorinated isocyanurate compounds or other chlorinated compounds that can generate a sanitizing or antimicrobial concentration of chlorine in the aqueous stream. Chlorine is a well known antimicrobial material and is often very effective in controlling microbial growth. However, the use of such chlorinating materials often has substantial drawbacks including equipment corrosion and hazard to operating personnel. The use rate of these chlorine-based antimicrobials is very high because they tend to be rapidly consumed by the high organic load in the aqueous stream. Further, upon consumption, compounds such as chlorine gas or chlorine dioxide decompose producing byproducts such as chlorites and chlorates, while hypochlorite produces trichloromethanes which may be toxic in very low concentrations. Lastly, chlorine dioxide is a toxic gas with an acceptable air concentration limit of 0.1 ppm. Exposure to ClO.sub.2 often leads to headaches, nausea, and respiratory problems, requiring expensive and intricate safety devices and equipment when it is used.
Iodophor antimicrobial agents have also been used for various aqueous antimicrobial applications. However, iodophor compounds tend to decompose or may be lost by evaporation when used in an aqueous medium. Thus, long term activity requires a high iodophor concentration.
As a result, a substantial need exists in the food processing industry to provide a means of food transport which also controls microbial soil load without the use of high concentrations of antimicrobials such as chlorine yielding compounds or other halogenated constituents.
A number of attempts have been made to rectify the problems caused by chlorinating substances in such materials. One attempt relates to the use of peracetic materials in flume water. Lokkesmoe et al., U.S. Pat. No. 5,409,713 teach the use of peracetic acid in an antimicrobial role in treating flume water. The use of other antimicrobial agents in the control of microorganisms is well known for various applications. For example, Grosse Bowing et al., U.S. Pat. Nos. 4,051,058 and 4,051,059 use peracetic acid as a food grade sanitizer in a variety of applications. Further, Greenspan et al., U.S. Pat. No. 2,512,640 teach the use of a peracetic acid composition comprising 500 ppm or more of peracetic acid for the treatment of various fruit and vegetable compositions in a spray applicator. Greenspan et al., Food Technology, Vol. 5, No. 3, 1951, similarly discloses spray compositions which may be applied to fresh fruits and vegetables comprising peracetic acid. Langford, U.K. Patent Application GE 2 187 958 A discloses the use of peracetic acid and propionic acid for the treatment of fungi in microbial plant pathogens on growing plants and especially edible crops. In other publications, Baldry et al., "Disinfection of Sewage Effluent with Peracetic Acid", Wat. Sci. Tech., Vol. 21, No. 3, pp. 203-206, 1989; and Poffe et al., "Disinfection of Effluents from Municipal Sewage Treatment Plants with Peroxy Acids", Zbl. Bakt. Hyg. I. Abt. Orig. B 167, 337-346 (1978) both disclose the use of peroxy acids for the treatment of effluents streams and municipal sewage applications. Hutchings et al., "Comparative Evaluation of the Bactericidal Efficiency of Peracetic Acid, Quaternaries, and Chlorine-Containing Compounds", Society of American Bacteriologists, Abstracts of Papers Presented at the 49th General Meeting, discloses the generally efficacy of peracetic acid compared to various other antimicrobial compounds. Additionally, Branner-Jorgensen et al., U.S. Pat. No. 4,591,565 discloses the reduction of the thermal stability of rennet through the use of aqueous-based aliphatic or inorganic peroxy acids. Block, "Disinfection, Sterilization, and Preservation", Fourth Edition, Chapter 9, pages 167-181, discloses the various characteristics and attributes of peroxygen compounds. However, generally the art has taught against the use of percarboxylic acids in aqueous streams due to concerns of compound stability in the presence of high concentrations of organic matter.
Hurst, U.S. Pat. No. 5,053,140 teaches a water treatment installation designed to remove solids, fat, bacteria and other impurities from water used in food processing. Bulk water is subjected to a number of purification steps including a countercurrent contact with a stream of ozone. Abiko, Japanese Patent Application Kokai No. 4-145997 teaches a similar purification unit. Avvakumov et al., U.S.S.R. Inventor Certificate No. 858735 and other patents teach the addition of ozone to fresh water input, or to clean make up water, to a food processing area or directly to the flume water transport area. Such schemes maintain a relatively high concentration of ozone in the bulk transportation water during movement of product from production locus to use locus. Beuchat, "Surface Disinfection of Raw Produce", Dairy Food and Environmental Sanitation, Vol. 12, No. 1, and other references teaches the use of the direct application of gaseous or aqueous ozone to bulk water to obtain microbial population control. T. R. Bott, "Ozone as a disinfectant in process plant", Food Control, generally discusses the use of ozone in general disinfectant applications. As a whole, Bott teaches the direct application of relatively small concentrations of ozone against surfaces for disinfecting and cleaning. Bott suggests relatively clean water with reduced ozone concentrations (about 0.1 ppm) for control. Sumi, JP 60-202229 and Shieno, JP 62-206536 contact food with preozonized aqueous solutions to effect microbial control. Shieno teaches a food sterilization method using preozonated solutions to affect microbial control in a system using circulated water that has no challenge load comprising microorganisms or soil. Shieno uses ozone with organic adjuvants having a relatively corrosive 3-5 pH. Lastly, Shieno apparently does not use a circulated/recirculated system. Sumi et al. teach a food washing, sanitizing device wherein ozone is dispersed into an open tank containing bulk water, i.e. greater than 50 wt. % of the service water. The treatment of the bulk water is done in an open container. Because of the disagreeable/toxic nature of ozone, contacting any food, or contacting a processing surface or an aqueous stream with ozone can cause worker discomfort or other problems. Further, attempts to treat large volumes of aqueous streams require substantial ozone generating equipment.
Typical commercial applications described for flume systems attempt microbial control using ozone applications into relatively clean, bulk--usually potable--make-up or filling waters. Other processes involve direct food contact between food and ozone. All of these applications are based on the premise that high demand, soiled waters will generally reduce or eliminate the ozone concentration and make ozone ineffective in high demand soiled waters for microbial control. Because of this concern that large concentrations of challenged soil load will prevent microbial control using ozone, the prior art has focused on treating clean water with ozone at or near the introduction of the make-up water into the flume system. These approaches result in potential ozone off gassing which can create hazard for operating personnel or equipment corrosion. Further, ozone in direct contact with food material can degrade the appearance or nutritive quality of the food. Further, these processes require relatively large consumption of ozone in such systems to maintain a high residual ozone concentration for effective microbial kill. Typically, an ozone residual goal of between 0.1-10 ppm ozone in water is required.
Accordingly, a substantial need exists for treatment systems that can effectively utilize ozone to control microbial populations without any direct contact of significant concentrates (greater than 1 ppm of ozone with large volumes of processing water, food articles, processing surfaces of the general environment surrounding the processing facilities. However, the use of ozone must successfully reduce microbial populations while not causing significant corrosion or other chemical attack on production facilities.